Retrofitting waste-heat recovery
A waste-heat recovery retrofit captures energy that currently leaves a plant as hot flue gas, exhaust or process streams and reuses it — typically to preheat combustion air, feedwater or a process flow. The key to a successful retrofit is matching the grade and timing of the recovered heat to a real, coincident demand.
What it is
Much of the energy a plant buys leaves as low- and medium-grade waste heat. A retrofit adds heat exchangers, economisers or air preheaters to an existing process to recover part of that heat and route it to somewhere useful, cutting the fuel or electricity bought to provide the same service.
Why it is done
Recovered heat displaces purchased fuel one-for-one, so the payback is driven by how many hours the recovery runs and how well the heat is used. It is a no-regrets decarbonisation step, but only if a genuine, simultaneous demand exists — recovered heat with nowhere to go saves nothing.
How it is done
Waste-heat sources are surveyed for temperature, flow and availability, and candidate sinks — feedwater, combustion air, space or process heating — are matched to them by grade and timing. A heat exchanger is selected and integrated, with controls to manage variable loads. Fouling and condensation risks (such as acid dew point in flue gas) are designed out, and performance is measured against the pre-retrofit baseline.
- Survey heat sources
- Identify sinks
- Match grade & timing
- Select exchanger
- Integrate & control
- Measure savings
What to watch for
Recovering heat with no coincident demand, and ignoring acid dew point when cooling flue gas below it, are the two errors that turn a good idea into a fouled, corroding liability.
Related practices
Running a compressed-air leak survey programme
Retrofitting variable-speed drives
Sequencing and controlling multiple compressors
Related topics
Waste Heat Recovery in Industry: Methods and Where It Pays · Heat Exchanger · Flue Gas Loss · Economiser
Common in: Chemicals · Steel & Metals · Cement · Paper & Packaging · Power Generation · Food Processing